1. Field of the Invention
The technology of electrical superconductors. Very recently the importance of materials which have superconducting properties has been constantly increasing. The discovery of new superconducting materials, in particular of the rare earth/Ba/Cu/O type resulted in an appreciable extension of the possible applications for superconductors since these substances become superconducting even at temperatures above 50K.
The invention relates to the further development and improvement of components composed of a ceramic high-temperature superconductor in wire form, it being intended to give consideration to the requirements of industrial mass production.
In particular it relates to an electrical conductor in wire or cable form composed of a sheathed wire or of a multiple-filament conductor based on a ceramic high-temperature superconductor of the REBa.sub.2 Cu.sub.3 O.sub.6.5+y' type, RE denoting a rare-earth metal and 0&lt;y&lt;1, or of the (La,Ba, Sr).sub.2 CuO.sub.4 type and the said superconductor being arranged as core in a metal sheath serving as mechanical support and emergency current conductor.
2. Discussion of Background
It is known to produce superconductors of the REBa.sub.2 Cu.sub.3 O.sub.6.5-7 type by preparing and mixing powders of the starting materials and subsequently heat treating them. The starting materials used are, as a rule, Y.sub.2 O.sub.3 /CuO and BaO or BaCO.sub.3. In the case of BaCO.sub.3, the CO.sub.2 has to be expelled by an additional calcination process (cf. T. Kawai and M. Kanai, "Preparation of high-Te Y--Ba--Cu--O Superconductor", Jap. Jour. of Applied Physics, vol. 26, No. 5, May 1987, pp. L736-L737; Y. Yamada, N. Fukuschima, S. Nakayama and S. Murase, "Critical current density of wire type Y--Ba--Cu oxide superconductor", Jap. Jour. of Applied Physics, vol. 26, No. 5, May 1987, pp. 2865-2866). In that case, sintering is carried out in an atmosphere (air) containing oxygen, that is to say under a certain O.sub.2 partial pressure. The surrounding sintering atmosphere thereby makes its contribution to achieving a slightly superstoichiometric oxygen content of the compound. It has already also been proposed to carry out the sintering process in a narrow silver tube. Silver is permeable to elementary oxygen so that the latter gets into the core material by diffusion (cf. H. Yoshino, N. Fukushima, M. Niu, S. Nakayama, Y. Yamada and S. Murase, "Superconducting wire and coil with zero resistance state at 90K and current density of 510 A/cm.sup.2 at 77 K", Toshiba Corporation, R+D Centre, Saiwai-Ku, Kawasaki City 210, Japan).
Ceramic high-temperature superconductors are remarkable for a relatively low critical current density, which is an obstacle to their general use. Apparently, even weak magnetic fields are sufficient to disable the superconduction. For this purpose, for example, even the self-magnetic field of the current-carrying conductor is sufficient. Ceramic material at present available is always limited by this self-field effect.